Effect Cancel

Fig. 1 Simple series interruption of the effected signal. The two resistors perform a simple passive summing function. In an actual design, the mixing function may be an active circuit. The concept is the same either way.

An effect cancel switch may refer to any type of switching scheme if the manufacturer just preferred the term "cancel" to "bypass," but on a technical level I consider any switch scheme that interrupts just the effect signal path to be an "effect cancel" type of bypass.

This is generally seen on effects that feature some variation on a "Blend" or "Mix" control. The "cancel" switch will somehow mute the effect signal, and just leave the dry signal alone.

Any type of effect could use this, but it is more commonly seen on delays and anything in the delay category (flangers, phasers, choruses, vibratos).

One benefit to this scheme is that a simple SPST can be used. This can simply interrupt the effect path by opening a connection somewhere. Less common, but totally possible, is that the SPST can mute the signal by shorting to ground.

Really elegant designs figure out how to use simple SPST or SPDT switches to toggle the effect and a LED. The Stereo Memory Man 7811B is a great example of this. The Electro Harmonix Small Clone EH 4600 comes to mind as well. Using a DPST or DPDT allows for easy toggling of both effect and LED.

Another benefit is that bypass/effect volume balancing is not an issue since we don't mess with the dry path.

The obvious drawback is that our signal is now always running through the pedal's circuitry. Sometimes this will be totally acceptable, and sometimes this will became a candidate for a "true bypass" mod. A lot of commercial pedals choose the "effect cancel" type scheme.

Dry Kill Mod

I've actually done the opposite of an effect cancel as a mod known as a "dry kill." This is again something you'd probably only do with a delay type effect. A "dry kill" switch will remove the input signal from the mix. Some delay pedals have a fixed amount of dry signal that is mixed in which can be undesirable when you want to route just the echoes somewhere.

To install a dry kill, you want to make sure that you only interrupt where the dry signal gets mixed into the final output. If you kill the signal too early, it may not reach the effect input. Also, if the signal always goes through this path to the output, you'll need to check that the normal bypass will still work even with the dry kill engaged. If not, performing a "true bypass" mod first is one possibility to keep things universal and simple. Otherwise, the footswitch bypass should take some sort of logical priority over the dry kill. For instance, if the dry kill opens the signal path, the footswitch could then override it when in bypass. This may end up seeming redundant when the dry kill isn't engaged, but would assure proper bypass operation.

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